1. Field of the Invention
This invention relates to a shift control system provided with a plurality of shift patterns for an automatic transmission of a vehicle.
2. Description of the Related Art
Conventionally, an automatic transmission of a vehicle is provided with a torque converter and a multi stage transmission gear mechanism connected with an output member of the torque converter. The transmission gear mechanism is provided with a plurality of shift gear stages of different speed ratios. A shift control unit is provided for making a shift operation to establish a proper shift stages automatically from among the plurality of shift gear stages in accordance with a vehicle operating condition.
The control unit is provided with a predetermined shift pattern for executing the shift operation between the plurality of the shift gear stages in accordance with vehicle speed and throttle opening, corresponding to the engine load, or throttle opening change speed, corresponding to the engine load change rate.
In a shift control provided with a single shift pattern, a shift operation, such as an up-shift operation or a down-shift operation, is made in light of the shift pattern when the vehicle speed and the engine load or the engine load change satisfies a predetermined relationship defined by the shift pattern.
It should be noted, however, that the vehicle operating condition is affected by road conditions, the personality of a driver and the like, as well as the shift pattern. As a result, in some cases, the shift operation is not properly made in response to an actual vehicle operating condition. In fact, the shift operation may be made contrary to the driver's desire.
In view of this, the shift control systems for automatic transmissions shown in Japanese Patent Publication Nos. 51-22698, published in 1976, and 57-8983, published in 1982 have been proposed. These publications disclose systems in which a plurality of shift patterns are provided for making shift operations so that one of the shift patterns is selected, for making a better shift operation, in accordance with a reference value of the engine load or the engine load change. In Japanese Patent Publication No. 51-22698, the shift pattern is switched in accordance with a throttle pedal stroke change speed corresponding to the engine load change rate. In Japanese Patent Publication No. 57-8983, the shift pattern is switched in accordance with the throttle opening or the engine load.
Generally, a conventional shift control system is provided with an economy mode shift pattern, in which the up-shift operation is made at a relatively low engine load to improve the fuel consumption efficiency, and a power mode shift pattern, in which the up-shift operation is made at a relatively high engine load to provide the vehicle with enough driving power.
However, the conventional shift control systems mentioned above execute the shift operation basically in accordance with the relationship between vehicle speed and engine load or engine load change so that the shift operation cannot be properly made in response to the driver's desire or when up-hill or winding roads and the like are present.